Fig. 5. Branchial arch arteries and adjacent dorsal aortae become narrowed in mice lacking Ccm1. (A-F) Immunohistochemical stains for the endothelial antigen Pecam on sagittal sections of embryos. Yellow arrows indicate one of the paired dorsal aortae; blue arrowheads highlight one of the paired branchial arch arteries. (A,B) No differences are observed between Ccm1^+/+ and Ccm1^-/- embryos at E8.0. A patent lumen is present in the bilateral dorsal aortae. A cord of endothelial tissue extends bilaterally from the aortic sac, through the branchial arch towards the dorsal aortae. (C,D) At E8.5, the Ccm1^+/+ embryo has formed a widely patent first branchial arch artery, whereas the branchial arch arteries of the Ccm1^-/- embryo fail to enlarge. (E,F) Further enlargement of these vessels is present at E9.0 in a wild-type embryo. The Ccm1^-/- embryo, however, is left with only a vestige of the branchial arch arteries and dorsal aortae. Scale bars: 100 µm.